Enterotoxins of V. cholerae and E. coli bind to mammalian cell membranes and produce an increased activity of adenyl cyclase. The multiplicity of effects observed depend on the end responses in the affected cell or tissue which are mediated by high levels of adenosine 3' 5' cyclic monophosphate cyAMP. We are investigating the nature of the binding of toxin to cells by the use of hormonal blocking agents, toxoids, and compounds which interact with gangliosides. We are also studying the possible role of the cyclic nucleotide regulating systems of bacteria to the production of enterotoxins. Assays for cyAMP, adenyl cyclase as well as for functions regulated in either bacterial cells or the cells of more complex organisms by this nucleotide are employed. A possible relationship is being sought between the role of enterotoxin in bacterial cells and its effects on mammalian cells.